CA2281207C - Process for extruding a hollow section or the like from a billet and a device for that purpose - Google Patents

Abstract

A process for extruding a section or the like from a billet is such that a billet is introduced into the bore of a container and, by means of an extrusion stem, is fed in the direction of extrusion into a shape-forming cross-sectional opening in a die. The billet material is pressed into a central inlet in the die and the resultant ductile mass fed outwards at an angle to the direction of extrusion through a plurality of channels to the shape-forming cross-section. The main load is applied by the extrusion force acting outside the central inlet and the shape-forming region and is preferably diverted outside the shape-forming region to the supporting die parts.

Description

Process for Extruding a Hollow Section or the Like from a Billet and a Device for that Pur ose The invention relates to a process for extruding a hollow section or the like from a billet which is introduced into the bore of a container and, by means of an extrusion stem, is fed in the direction of extrusion into a shape-forming cross-sectional opening in a die.
Furthermore, the invention also relates to a device which is specially suited for that purpose.
During extrusion a material which is in a ductile: state - in the case of metals this includes 1o materials such as non-ferrous metals, sintered medals or steel but in particular material in the form of an aluminium alloy - viz., a heated cast billet or rolled bar of material, is pressed in the direction of extrusion by an extrusion stem -- or in the case of hydrostatic extrusion, by means of a fluid - out of a container through one or more shape-forming openings in a die.
In the case of direct or forward extrusion the stenn moves in the direction of the die opening, in the same direction as the resultant section. In indirect or backward extrusion the material is moved in the direction counter to that of the stem, through a die which is mounted on the hollow stem.
To produce hollow sections so called hollow dies with a die plate are employed in the 2o extrusion process, an example of this is described in DE 24 46 308 Al. The die plate is integrated in a part of the mandrel to provide the outer contour of the resultant section. In that case, in order to shape the inner contour, a mandrel - in the case of mufti-chamber sections a plurality of mandrels - is arranged such that the mandrel projects into the die plate and beyond the shape-forming region. In such a process the ductile material is guided over inlets and into the extrusion tool in such a manner that the strands from the individual inlets flow together again under mandrel support arms - into a welding chamber - where they are welded together again. As the extrusion process proceeds further, the material or the aluminium alloy flows past the mandrel and the dlie opening, thereby adopting the prescribed hollow section shape. The inlets are always situated outside around the hollow space or 3o spaces in the section; the aluminium alloy is introduced into the shape-forming region of the die from the outside, in particular via a plurality of inlets. If in the case of mufti-chamber dies the inner regions of the hollow section can not be adequately supplied with metal from outside, then additional feeding inlets are provided in the inner part of the hollow section.
The main supply inlets are always situated around the outer contour of the hollow space in the section.

The size of hollow section that can be manufactured i.e. its maximum diameter of circumscribing circle is limited therefore by the diameter of the container and the size of the inlets arranged around the hollow space as well as the strength of the above mentioned mandrel support arms.
In general, the maximum size of section that can be manufactured on conventional extrusion presses is limited by the size of the extrusion press, the diameter of the container used and the strength of the extrusion die. The above mentioned patent DE 24 46 308 and patent DE 28 12 690 of the applicant are concerned with the dimensioning of the latter for hollow section manufacture using large mandrel surface area.
Also the quality of the extrusion weld is influenced by the outer edge zone of the extrusion billet flowing into the outer inlets in the extrusion die, with the result that it is possibly necessary to machine away the outer skin of the billet before use.
Furthermore, the shaping capacity and the service life of the extrusion tool are considerably reduced by the high load on the mandrel surface, by creep resulting from this high load, and by bending.
1 S Attention must also be given to the fact that metal billets, especially billets of aluminium alloys, are covered with contaminants - for example residual lubricant - and with an oxide layer. In particular oxide particles on the end and outer surface of the ingot may be extremely detrimental with respect to the structure of the section; the resultant zone of contaminating inclusions in the section is relatively long - depending on the shape of the section and the extrusion speed. Consequently, with increasing quality requirements, manufacturers are forced to scrap increasingly longer lengths of section. The result is diminished output and lower cost efficiency due to diminishing yield of section length.
SUMMARY OF THE INVENTION
The present invention seeks to enable section widths to be manufactured with maximum independence on extrusion press geometry. In addition, contaminated regions which arise during extrusion, in particular extrusion of aluminium alloys, should be prevented.

-2a-In accordance with one embodiment of the invention there is a process for extruding a hollow section from a billet which is introduced into the bore of a container and, by means of an extrusion stem, is fed in the direction of extrusion into a shape-forming opening in a die, whereas, the billet material is pressed into a central inlet in the die and the resultant ductile mass fed outwards at an angle to the direction of extrusion through a plurality of channels to a shape-forming cross-section, characterised in that, a main load is applied by an extrusion force acting outside the central inlet and a shape-forming region, and is diverted to die-supporting parts.
In accordance with another embodiment of the invention there is a device for extruding a hollow section (12, 12k, 12,p, 12X) from a billet (24) which is fed into the bore (22) of a container (18) and is pressed by an extrusion stem (16) in the direction of extrusion (x) into a shape-forming cross-section (70) of a die (32, 32a, 32b), of its inlet end (62) into the die (32, 32a, 32b) an approximately central inlet (64, 64a) is provided within an extension to the hollow space in the section, that a ,plurality of arm-like channels (66) run from a wall (65) and connect to the shape-forming cross-section (70) for the purpose of performing the process according to any one of the claims 1 and 2, characterised in that, the inlet (64) is blunted-cone shaped in the direction of (x), the inlet (64) comprising the valve (65) and an axis M, said wall (65) and axis M form an acute angle.

According to the invention the billet material is introduced under pressure into a central inlet in the shape-forming die and the resultant ductile mass fed outwards at an angle to the direction of extrusion through a plurality of channels to the shape-forming section. The extrudate therefore no longer reaches the shape-forming region via inlets arranged around the hollow section, but instead is fed through a central inlet opening in the interior of the space in the hollow section. The extrudate flows according to the invention from this central inlet, out via the radial, outward inclined channels of a large welding chamber into the shape-forming region.
1o The diameter of the circumscribing circle of t:he section to be manufactured may be significantly larger than the diameter of the container.
Also within the scope of the invention is a device for extruding a hollow section or the like from a billet which is introduced into the bore of a container and is fed by means of an extrusion stem in the direction of extrusion to a shape-forming cross-sectional opening in the die, whereby from the inlet side of the die a.n approximately central inlet is provided within the hollow space of the section; from the wall of that inlet a plurality of arm-like channels branches out at an angle of preferably more than 90° to the die end face; joining up to these is the shape-forming cross-sectional opening which is preceded by a welding chamber.
In the case of rotationally symmetrical sections the central inlet is preferably in the centre of the die. In the case of irregularly shaped sections the centre of gravity of the area of the inlet is situated as close as possible to the centre of gravity of the section or in the middle of the die - or in another suitable region of the hollow space in the section.
If hollow sections with large side-length ratios or asymmetric shape have to be produced, then the necessary amount of metal feed is achieved by means of a further feature according to the invention viz., via at least two of the described central inlets which form the 3o respective central inlet element for the channels running at an angle out of them.
In the case of certain extrusion cross-sections it may be necessary in special cases to provide, in addition to the central inlet, material feed channels also outside the central inlet or hollow section space, this in order to feed particular parts of the section. In all of these special cases the so-called central inlet also serves as the main inlet; these metal feed channels are simply supplementary.

The production of round tubes of different diameter and wall thickness may be performed using basic central inlet dies in which, advantag;eously, mandrel rings of different outer diameter and die plates of different internal diameter are provided in predetermined cross-sectional regions.
One of the advantages achieved by the procedure according to the invention is that the size of section that can be produced is not limited in its geometry by the size of the extrusion press and diameter of the container. Tubes or hollow sections of large circumscribing circles 1o can also be manufactured using small diameter containers on extrusion presses having relatively small extrusion force as the amounts of extrudate necessary for deformation can be fed to the shape determining zone via central inlets of small cross-section - i.e. openings of small diameter. It is therefore possible to manufacture sections with small cross-sectional area and large diameter of circumscribing circle also using materials that are difficult to shape, and to do so using small containers and high specific pressure; as a result the spectrum of cross-sections that can be produced is greatly increased.
Of particular importance is that the material is alvrays fed to the die from the middle of the billet and is not spread out to the shape-forming; region of the die until in the die itself.
2o Extrudate from the contaminated outer region of billet can not flow into the die. The material from the contaminated outer edge zone is collected in the ingot butt and sheared off at the end of the extrusion stroke. As a result, using the die according to the invention it is basically no longer necessary to machine away tile outer region of the billet -as may be necessary when extruding large cross-sections in old extrusion presses.
The load acting on the die is much lower in the region which is important for shaping the section viz., in the mandrel interior; this because: the load is applied only over the cross-sectional opening of the central , and not as in the case with conventional dies over the whole cross-sectional surface on the section hollow spaces projected on the die inlet side.
The main load applied to the cross-section of the billet to be extruded occurs in the die region outside the central inlet or inlets. This load may be taken up by the outer region of the die. i.e. not the shape-forming region - or by the die support parts.
The low load on the die in the process according tot the invention results in accurately dimensioned extruded sections over a longer service life of die, or for the same service life permits the production of lighter section cross-sections or such using materials that are difficult to extruded.
Further advantages, features and details of the invention are revealed in the following description of preferred exemplified embodiments and with the aid of the drawing which shows in Fig. 1: a perspective view of part of an extrusion press with horizontal stem;
1o Fig. 2: a sectioned view of part of another extrusion press enlarged with respect to figure 1;
Fig. 3: a schematic epresentation of a longitudinal section through a container of the extrusion press with stem followed, in the direction of extrusion, by a die;
Fig. 4, 5,6: the representation shown in figure 3 but with container and stem in different positions;
2o Fig. 7, 9,11,13: schematic end views of various, different extrusion dies;
Fig. 8, 10, 12, 14: cross-sections through figure 7 along line VIII-VIII, through figure 9 along X - X, through figure 11 along XII-XII and through figure 13 along XIV-XIV
Fig. 15: a longitudinal section through a shape-forming die showing the influence of load thereon;
Fig. 16 a perspective view through a partially sectioned die.
An extrusion press 10 for direct extrusion of sections 12 features, as shown in figure 1, on a main cylinder 14, an extrusion stem 16 which lies, along the longitudinal axis A of the bore 19 of a recipient or container 18. The diameter d of a dummy block 17 at the free end face of the stem 16 is slightly smaller than the free bore diameter dl with the result that the stem 16 is able to penetrate the container bore. The mentioned free bore diameter dl is delimited by the inner surface 20 of a sleeve 21 inserted in the container 18 or its bore 19. In the following the space inside this sleeve 21 is called the container bore 22.
The maximum distance between the front 23 of the; container and the dummy block 17 in the inactive position of the stem 16 - which is not shown here - is such that a billet or ingot 24 of light weight metal, in particular preheated aluminium alloy, can be aligned by means of a loader 26 in front of the container bore 22 and pushed by the stem 16 in the direction of extrusion x into the container bore 22.
1o Close to a container end face 23a, remote from the stem 16, is the shape-forming die 32 resting in a die holder 28 on an extrusion platen 30. With respect to the direction of extrusion x this is followed by a run-out channel 34 in the platen 30 through which the resulting section 12 - having the shape endowed by the contour of the die 32 -is removed.
Above the container 18 is, as shown in figure 1, a jacking system 36 for a shearing facility 38 which moves radially to a gap 40 between the container 18 and the die 32.
In the example shown in figure 2 a mandrel part 33 is provided between the container 18 and the plate-shaped die 32, this for the purpose of creating the inner contour of a resultant section 12a. The die plate lies - in the direction of extrusion x -immediately downstream of 2o a bolster plate 42 in a bolster plate holder 44. A ring-shaped collar 46 is situated adjacent to the bolster plate 42 followed by a closing ring 48 in the platen 30. A die container 50 is provided for the die holder 28, bolster plate 44 holder and ring-shaped collar 46.
At the end of the extrusion process a so-called butt 52, from which the dummy block 17 has already separated, forms on the facing die surface at the end of the container bore 22 away from the stem 16. As a result of a collar 54 of oversize h on container sleeve 21, that tool face remains a distance from the front end 23a of the container. Also at the rear container end 23 the container bore 22 surrounds a ring-shaped collar 56 which provides a projecting length of the container sleeve 21.
On inserting a new billet 24 the free end of the butt 52 is e.g. about 80 mm thick. The back end distance a of ingot material amounts to at most 20 mm.
The container 18 is then drawn back - e.g. somewhat more than 450 mm - until the butt 52 is standing free (fig. 5). If the billet 24, as shown in figure 6, projects out a collar length t of about 10 mm beyond the collar 54, then the billet 24 is compressed by the stem 16; it should _7_ then not be possible for the billet 24 to be displaced by the shearing tool 38 as a result of a subsequent shearing step. Before the shearing proc;ess takes place, the container 18 is drawn counter to the direction of extrusion x until the rear face of the shaping tool or die 32 is a distance from the end face 23a of the container 18. The container 18 and the die 32 are temporarily fixed in this position.
By lowering a shearing blade of shearing tool 38 - shown in figure 1 - the butt 42 or an end slice 58 of projecting length t of billet 24 are removed simultaneously, and with that the end face 60 of the billet 24 facing in the direction of extrusion x ; prior to the mentioned shearing operation an oxide layer formed at the end face 60, the oxide particles of that layer would create undesirable impurities in the resultant section 12. By removing the end slice 58 along with the end face 60 of the billet a billet end free of oxide layer is obtained.
After the shearing operation the container 18 is again moved towards the die 32 and the extrusion process can begin again from the start.
Figures 7, 8 show a plate-shaped forming tool or die 32 of diameter n - equal here to approx.
500 mm - comprising two die parts 31, 31a for the purpose of manufacturing a rotationally symmetrical tube 12 or the like hollow section of circular cross-section of inner diameter q, 2o here 236 mm in magnitude. As viewed in the direction of extrusion x a so called central inlet 64 which is blunted-cone in shape, is provided in l:he mandrel or die part 31 in the end 62 to the die facing the mandrel; the die axis M forms thereby the axis of symmetry;
the diameter d2 of its inlet contour K measures 170 mm. Branching out from the inlet wall 65, which runs at an angle w - here 65° - from the end face 62 of the die, are arm-like channels 66 the outer channel contour 67 of which in this section runs aipproximately parallel to the diametrically distant contour of the inlet wall 65 and form an angle wl with the other visible neighbouring contour of the inlet wall 65 - here an angle of 50°. These channels 66 -tapering in the plan view shown in figure 7 ultimately to dome-like end section 66e - terminate in the direction of extrusion x in a ring-shaped welding chamber E.8 which is followed by a circular shaping cross-section 70 of width z for the corresponding vvall thickness of the tube 12X. The shaping cross-section 70 is limited on the inside by the surface 72 - here ring-shaped - of a mandrel projection 74.
The extrudate is therefore not - as is normally the case - fed to the shaping region through a plurality of inlets situated outside around the hollow section or tube 12, but instead only via that central inlet 64. During the subsequent extension process the extrudate is fed via the -g_ radially inclined channels 66, 66a out of the central inlet 64 outwards to the welding chamber 68 and to the shape-giving cross-section '70.
In the case of irregular shaped sections the areal centre of gravity of the inlet is situated as close as possible to the centre of gravity by mass of the section or in the middle M of the die - or in another suitable region of the section hollow space.
As shown in figures 9 and 10 hollow sections 12~P may also be created with a polygonal or asymmetric cross-section using a central inlet 64a. The inlet wall 65, shown in figure 10, to creates an asymmetric cross-section i.e. the die a;~cis M lies outside the inlet axis Ml. With such asymmetric section shapes or hollow sections 12p or 12k with large side length ratios the necessary amounts of material can be fed via at least two of the described central inlets 64, as indicated in the die shown in figures 11 and 12. There the central axes Ml of the central inlets 64 run a radial distance k from the die axis M.
The production of round tubes 12 of different diameter q and wall thickness y can be per-formed using dies 32a in which mandrel rings 76 of different outer diameter and die plates 31a of different inner diameter are employed in prE;detel-mined cross-sectional regions.
In figure 15 it can be seen that the load P on the die is much lower in that region which is important for creating the section viz., in the interhor of the mandrel part 31, this because the load is created only over the cross-sectional opening of the central inlet 64 and not - as in conventional dies - over the whole cross-sectional surface of the section hollow space areas projected onto the die inlet side 62.
The main load over the cross-section of the billet to be extruded takes place in the die area outside the central inlet or inlets 64. This load can, as indicated by the arrows Q, be borne in the outer region of the die 30 - i.e. not in the shapiing region - by the die support parts.
The perspective view in figure 16 of a mandrel part 31 of a die 32 shows clearly its make up with central inlet 64, the subsequent channels 66 and a plate-shaped mandrel projection 74 which projects out at the central axis of the die and determines the inner surface of the section and with that also the inner limit 72 of the shape-forming opening 70.

Claims (14)

1. The process for extruding a hollow section from a billet which is introduced into the bore of a container and, by means of an extrusion stem, is fed in the direction of extrusion into a shape-forming opening in a die, whereas, the billet material is pressed into a central inlet in the die and the resultant ductile mass fed outwards at an angle to the direction of extrusion through a plurality of channels to a shape-forming cross-section, characterised in that, a main load is applied by an extrusion force acting outside the central inlet and a shape-forming region, and is diverted to die-supporting parts.

2. A process according to claim 1, characterised in that sections are manufactured with a larger diameter of circumscribing circle than the diameter of the container.

3. A device for extruding a hollow section (12, 12k, 12p, 12x) from a billet (24) which is fed into the bore (22) of a container (18) and is pressed by an extrusion stem (16) in the direction of extrusion (x) into a shape-forming cross-section (70) of a die (32, 32a, 32b), of its inlet end (62) into the die (32, 32a, 32b) an approximately central inlet (64, 64a) is provided within an extension to the hollow space in the section, that a plurality of arm-like channels (66) run from a wall (65) and connect to the shape-forming cross-section (70) for the purpose of performing the process according to any one of the claims 1 and 2, characterised in that, the inlet (64) is blunted-cone shaped in the direction of (x), the inlet (64) comprising the valve (65) and an axis (M), said wall (65) and axis (M) form an acute angle.

4. The device according to claim 3, characterised in that a plurality of arm-like channels (66) run from the wall (65) of the inlet (64) at an angle (w + w1) of more than 90° to the end face (62) of the die, and these channels (66) are followed by a welding chamber (68) which in turn connects up with the shape-forming cross-section (70).

5. Device according to claims 3 or 4, characterised in that the channels (66) taper to a dome-like end section (66e).

6. Device according to any one of claims 3 to 5, characterised in that the wall (65) of the central inlet (64) together with the end face (62) embrace an angle (w) of 65°.

7. Device according to any one of claims 3 to 6, characterised by an angle (w1) of 50° between the wall (65) of the inlet (64) and the outer contours of welding chamber (68) of channels (66).

8. Device according to any one of claims 3 to 7, characterised by a ratio of the inner diameter (q) of the shape-giving cross-section (70) to the diameter of the inlet contour (d2) of 1.4.

9. Device according to claim 3 or 4, characterised in that the central inlet (64) for a rotationally symmetric section (12x) is situated approximately in the middle (M) of the die (32).

10. Device according to claim 3 or 4, characterised in that the central inlet (64) for a section (12k, 12p) of irregular contour is situated approximately at the centre of gravity according to section mass or at the middle of the die.

11. Device according to claim 10, characterised in that the die axis (M) lies adjacent an inlet axis (M1).

12. Device according to one of the claims 3 or 4, characterised in that at least two neighbouring inlets (64) of the die (32a) are respective central inlet elements for the channels (66) running out from them.

13. Device according to claim 12, characterised in that the inlet axes (Ml) of the inlets (64) run a radial distance (k) from a central axis (M).

14. Device according to any one of claims 3 to 13, characterised in that its shaping die (32b) features exchangeable mandrel rings (76) of different outer diameter and die plates (31a) of different inner diameter (Fig. 13, 14).